This chapter fleshes out the concept of inheritance intro-

duced at the beginning of this textbook (1.1).

You will also draw on what you have learned about

diploid and haploid sets of chromosomes (18.1) and how

gametes form during meiosis (18.7).

Key ConCepts

LinKs to earLier ConCepts

Genes and Inheritance

Genes are segments of DNA that

code for inherited traits. Genes

have different forms called alleles.

A gamete carries one copy of each

gene. Sections 19.1–19.2

Basic “Rules” of Inheritance

Traits coded by a single gene are

inherited according to the rules of

probability (chance). The paired

copies of a gene on one chromo-

some are sorted into gametes

independently of genes on other

chromosomes. Section 19.3

Gene Effects

Inheritance often is unpredict-

able. Examples include the many

traits that are determined by more

than one gene, and genes that

may affect several traits. Sections

19.4–19.5

373

Got freckles? Freckles are common in fair-skinned

people, especially individuals who also have red hair. Each freckle is

a spot where the skin pigment melanin is especially concentrated.

Although the tendency to develop freckles is controlled by a single

gene, as with most characteristics the full story is more interesting.

Researchers have discovered that other genes influence the color,

pattern, and even the number of a person’s freckles. In this chapter

we turn to basic concepts about genes and how they produce all the

biological traits we inherit from our parents.

introduCtion to GenetiCs

19

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